Strange selection behaviour from 2.8 to 2.79b
This is happening because of incompatibility between the two versions. 

Blender 2.80 differs from 2.79 a lot. The two versions are not 100% compatible. You should not work in 2.79 with data saved or made in 2.80 or you will experience some issues, like for example this what you are seeing in this case. 

If you only need to get simple geometry made in 2.80 to work in 2.79, you can export the models in some other format like .obj and import them to 2.79. It will work fine this way. However if you needed to export more complex things like materials, normal data, animation, rigs and other things you may experience a lot more problems and it might not be possible/practical to solve those. It is best to choose a version and stick with it in one project.